Apparatus for maintaining constant peripheral speed of a grinding wheel to compensatefor wheel wear



Dec. 10, 1963 R. v. SCHNEIDER ETAL 3,

APPARATUS FOR MAINTAINING CONSTANT PERIPHERAL SPEED OF A GRINDING WHEELT0 COMPENSATE FOR WHEEL WEAR Filed Aug. 11, 1961 /a, le

' AMPU HER ELECTEO -TEANSM ITTER ATTORNEY United States Patent APPARATUSFGR MAiNlAINlNG CGNSTANT PERIPHERAL EEPEED @F A GRINDING WHEEL TCCGMPENSATE FOR WHEEL WEAR Robert V. Schneider and Lennart A. Kasparson,both of Wei-caster, Mass, assignors to Norton Company, Worcester, Mass,a corporation of Massachusetts Filed Aug. 11, 1%1, Ser. No. 139$ 14-Claims. (Cl. 51-1345) This invention relates to grinding machines andhas for its principal objects to provide mechanism for automaticallymaintaining the surface speed of a grinding wheel substantially constantto compensate for wheel wear; to provide a mechanism which will increasethe speed of rotation of the Wheel in proportion to its reduction inradius due to wear without overcornpensation; to provide mechanism inwhich there is means for stopping the wheel in the event of an abruptchange in the mass of the wheel of the order resulting from thebreaking-out of a chunk of abrasive material from the wheel, or offailure of some component part of the apparatus, which induces excessivespeed without interfering with the means which merely modifies therotation to maintain a constant surface speed; to provide a mechanismwhich has maximum and minimum speed limits, so that the machine willfail safe; and to provide mechanism which is adapted to be used inconjunction with conventional grinding machines without extensivealteration thereof.

As herein illustrated, the apparatus comprises a sensing deviceresponsive to a reduction in the radius of the wheel due to Wear toproduce a signal of increasing amount, compensating means operable by anincrease in the signal to increase the speed of the motor to maintainthe surface speed of the wheel constant as the wheel diminishes radius,and means operable, by an increase in speed of the motor which issufiicient to maintain the surface speed of the wheel constant, tonullify the effect of the increase in the signal until the diameter isfurther reduced by wear. There is also a safety mechanism disposed at aposition adjacent the wheel, but spaced therefrom a predeterminedamount, and maintained at said predetermined distance by each increasein the speed of the motor as the latter is speeded-up to maintain thesurface speed of the wheel constant, which is movable into engagementwith the wheel in the event of an excessive increase in speed caused byfailure of a component part of the mechanism, or damage to the wheel, tostop the motor, and there are limit switches to render the mechanisminoperable in the event of too high or too low speeds.

The invention will now be described in greater detail with reference tothe accompanying drawings wherein:

FIG. 1 is an elevation of the face of a grinding wheel, showing thesensing means supported at the opposite sides thereof;

FIG. 2 is a wiring diagram of the control circuit; and

FIG. 3 is a diagrammatic illustration of the wheel, the wheel drivemotor, and a safety device for rendering the mechanism inoperative inthe event of excessive speed.

Referring to the drawings, there is shown a grinding Wheel mounted on ashaft 12 for rotation about a horizontal axis, the shaft being connectedto a drive motor M, as diagrammatically shown in FIG. 3.

Grinding wheels of large diameter and high speed, such as are used forsnagging large steel billets and slabs wear rapidly and to maintain anefiicient grinding speed, it is necessary to constantly increase thespeed of rotation of the wheel in proportion to its reduction indiameter by reason of wear. In accordance with this invention a sensingdevice is provided for this purpose which, as

shown in FIG. 1, includes a source of radiation 14 mounted at one sideof the Wheel and a radiation pick-up device 16 mounted at the oppositeside of the wheel. The source of radiation 14a is situated at a radialdistance from the axis of rotation, substantially equal to the radius ofthe wheel prior to wear, and its beam is controlled by an aperture sothat it has an angle of spread which, projected on the side of thewheel, is substantially equal to the permissible radial wear of thewheel before the latter has to be renewed, as indicated by the dimensiona. The pick-up device 16, which is shielded from the source of radiationby the wheel, is of such a character that it generates a signal whichincreases in magni tude in proportion to the decrease in radius of theWheel as the latter is worn down, and thus exposes the device 16 to moreand more radiation.

The parts 14 and 16 of the sensing device are manufactured by theIndustrial Nucleonics Corporation of Columbus, Ohio, and arecommercially available according to specification. The part 14 comprisesa heavy casting provided with a manually operable shutter notillustrated for closing a radiation aperture, en not in use, andcontains, as a source 142, two milligrams of radium 226. The part 16comprises a pipe section within which is mounted a long lifehalogen-quenched stainless steel shell Geiger-Mueller tube notillustrated, which is operable to convert gamma radiation into electricsignals.

For maximum safety in this application, the manually operable shutterprovided in part 14 by the manufacturer may be interlocked with themeans for securing the cover on the guard enclosing grinding wheel 16)by a suitable linkage so that the shutter is closed automatically whenthe cover is released. With the provision of such an arrangement, themachine operator is fully protected against radiation automaticallywhenever the wheel guard is opened for the purpose of changing thegrinding wheel.

The electric signal produced by the sensing device is used to controlthe speed of the variable speed wheel drive motor M by way of a controlcircuit. shown in FIG. 2. Power is supplied to the circuit from a voltAC. source. The electric current provided by the sensing device isamplified by an amplifier 18 and fed to an electrotransmitter 29. Theelectrotransrnitter 26 operates to move the slider 21 of a potentiometer22 from right to left on its resistor 23 as the wheel wears. Since thesensing device operates continuously a speed compensator 26 is providedto stabilize the speed of the motor when the wheel reaches a speed whichcompensates for the decrease in radius. To this end, the potentiometerresistor 23 is placed in a secondary circuit containing the compensatorand is supplied with alternating current from the secondary winding 27of a transformer, the primary winding of which is shown at 29. Thecompensator circuit includes a thyratron tube 28, a tachometer generator35, and a relay CR1. A rectifier is provided for converting thealternating current to direct current, so that when the slide 21 of thepotentiometer, which is connected to the grid 30 of the thyratron tube,is moved in a counterclockwise direction in response to an increase inradiation, direct current will be supplied to the grid of the thyra trontube. By making the grid positive, it conducts current so as to energizethe relay CR1. Energizing relay CR1 closes a switch SCR1 of a thirdcircuit which contains the field winding 34 of a rheostat positioningmotor 35. The positioning motor 35 drives a rheostat 37 (FIG. 3) whichcontrols the current supplied to the wheel motor M, in a direction toincrease the speed of the motor provided that the switch SW1 is set inthe run position and the normally closed limit switch LSH is closed. Thetachometer generator 36 is also connected to the grid 30 of thethyratron. The tachometer is driven by the motor M so that its speedincreases with that of the motor.

Rotation of the tachometer 36 generates a negative current which changesproportional to the increase in the speed of the motor and feeds it backto the grid 39 of the thyratron tube. When the speed of the motor issuch that the negative current generated by the tachometer balances thepositive current supplied to the grid from the potentiometer, flow ofcurrent through the tube is stopped, thereby de-energizing the relayCR1. De-energization of the relay opens the switch SCRl so that thepositioning motor 35 comes to a stop and the motor M will continue torun at a constant speed even though the radiation pick-up devicecontained within part 16 continues to be receptive of radiation from theradiation source 14a. This stabilized condition will continue until moreof the surface of the wheel is worn away, thereby increasing the amountof radiation received by the radiation pick-up device, which results innnbalancing the thyratron tube on the positive side, so as to restartthe positioning motor 35 and to move the field rheostat 37 in adirection to further increase the speed of the motor. The circuitexplained is in the form of a balancing device or governor.

The normally closed limit switch LS H is controlled by an actuator notillustrated when the slider of the rheostat 37 is rotated into theposition which produces the highest permissible speed for the wheeldrive motor M so that the run circuit which produces rotation of thepositioning motor 35' to increase the speed of motor M is deenergizedwhen motor M reaches this maximum speed.

Similarly, the normally closed limit switch LSL in cluded in the resetcircuit for the positioning motor 35 is opened by an actuator notillustrated when the slider of the rheostat 37 is rotated into theposition which produces the lowest required speed of the motor M.

A safety device 38 (FIG. 3) is provided for shutting down the apparatusin the event of failure of some component part thereof, or of the wheelitself, which causes excessive speed of the motor M. As shown, thiscom.- prises an arm 40 fixed to the shaft 42 which connects theposition-ing motor 35 to the rheostat 37, so that it is rotated inproportion to the rotation of the rheostat 37. The arm 40 [has pivotallyconnected to it one end of a link 44, the other end of which ispivotally connected to a rod 46 which is supported with its distal endat a predetermined distance from the surface of the grinding wheel. Alimit switch LS1 is mounted at the distal end of the rod 46 and has onit an actuator 48 which is maintained at a predetermined distance fromthe surface of the wheel during normal operation of the apparatus and ismoved toward the wheel in proportion to the reduction in the diameter ofthe wheel. In the event, however, that the signal produced by thesensing device is not compensated for by the signal produced by thetachometer due to some failure in the circuit or possibly by breakage ofthe wheel, the unchecked continuing rotation of the positioning motorwill move the rod 46 and hence the switch actuator 48 into engagementwith the wheel and thus open the limit switch LS1, cutting off the mainpower supply to motor M and shutting down the grinding machine.

It is within the scope of this invention to employ photoelectric,pneumatic or sonic sensing devices for producing a signal to effectoperation of the compensator and correspondingly to employ anyelectrical, pneumatic, or mechanical equivalent of the compensator toeffect control of the motor.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

We claim:

1. Ina grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining the surface speed of the Wheelconstant as the wheel Wears, comprising an elongated sensing devicefixedly secured radially of the grinding wheel and operable, in responseto a reduction in the radius of the wheel, to produce a signal ofincreased magnitude, a compensator responsive to an increase in thesignal to increase the speed of the motor, and a feed-back operated bythe motor in response to an increase in the speed of the motorsufficient to maintain the surface speed of the wheel constant tonullify the effect of the increase in the signal.

2. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining e surface speed of the wheelconstant as the wheel wears, comprising an elongated sensing devicefixedly secured radially of the grinding Wheel and operable, in responseto a reduction in the radius of the wheel, to produce a signal ofincreased magnitude, means operable to increase the speed of the motor,a compensator operable to effect operation of the last-named means,operation of said compensator being effected by an increase in thesignal, and a feed-back operated by the motor in response to an increasein the speed of the motor sufiicient to maintain the surface speed ofthe wheel constant to nullify the effect of the increase in the signal.

3. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining the surface speed of the wheelconstant as the wheel wears, comprising a sensisng device responsive toa reduction in the radius of the wheel to produce a signal of increasedmagnitude, a thyratron tube, a potentiometer responsive to an increasein the signal to make the thyratron tube conductive, a tachometeroperable, by an increase in the speed of the motor, sufiicient tomaintain the surface speed of the wheel constant to make the thyratrontube non-conductive, and means operable, when the tube becomesconductive, to elfect an increase in the speed of the motor.

=4. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining the surface speed of the wheelconstant as the wheel wears, comprising sensing means having componentsfixedly disposed so that they face opposite faces of the wheel, saidcomponents including a source of radiation and an elongated sensingelement disposed radially of the grinding wheel, said sensing elementbeing responsive to an increase in exposure to said source of radiationby wear of the wheel interposed therebetwcen to produce a signal ofincreasing amount, a device operable in response to an increase in thesignal to increase the speed of rotation of the motor to compensate forthe reduction in radius of the wheel, and means driven by the motoroperated by an increase in. the speed of the motor sufficient tomaintain the surface speed constant so as to neutralize the increasedsignal.

5. In a grinding machine, a grinding wheel, a motor for driving thewheel and means for maintaining the surface speed of the wheel constantas the wheel wears, comprising sensing means having components fixedlydisposed adjacent opposite faces of the wheel consisting respectively ofa fixed radiation source and a fixed elongated sensing element disposedradially of the wheel which are increasingly exposed to each other asthe radius of the wheel diminishes, said means operating to produce asignal of cumulatively increasing amount as the radius of the wheeldiminishes, la rheostat controlling the supply of current to the motor,means operable, in response to each increase in the signal, to move therheostat in a direction to increase the speed of the motor, and meanscoupled to the motor operable by an increase in the speed of the motorsufiicient to maintain the surface speed constant to produce acumulatively increasing compensating signal effective to neutralize theincreased signal produced by said sensing means.

6. In a grinding machine, a grinding wheel, a wheel motor for drivingthe wheel and means for maintaining said surface speed of the wheelconstant as the wheel wears, comprising a fixedly mounted sensing deviceoperable to produce a signal of cumulatively increasing magnitude as thewheel diminishes in radius, a field nheostat for supplying current tothe motor, a positioning motor for effecting movement of the rheostat,means operable by an increase in the signal to effect operation of thepositioning motor and hence movement of the rheostat in a direction toincrease the speed of the wheel motor, and means operated by the motorin response to an increase in speed of the wheel motor suflicient tomaintain the surface speed of the wheel constant to produce acumulatively increasing compensating signal effective to neutrailize theincreased signal produced by said sensing means.

7. In a grinding machine, a grinding wheel, a motor for dniving thegrinding wheel and means for maintaining the surface speed of the wheelconstant as the wheel wears, comprising fixedly mounted sensing meansoperable to produce a signal of constantly increasing magnitude as thewheel wears, a field rheostat for supplying current to the motor, apositioning motor for moving the rheostat, a positioning motor switch,means operable in response to an increase in the signal to close saidswitch, and means operated by the wheel motor in response to an increasein speed of the wheel motor sufiicient to maintain the surface speed ofthe wheel constant to produce a signal of opposite kind and of amagnitude sufiicient to neutralize said first-named signal and therebyopen said switch.

8. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining said surface speed of the wheelconstant as the wheel wears, comprising sensing means including afixedly mounted radiation source and a fixedly mounted radiation pick-updisposed adjacent opposite faces of the wheel, said pick-up having asensitive Zone disposed radially of the wheel and at least as long asthe permissible radial wear of the wheel, and said source having adispersion angle such that its projection on the side of the wheelcorresponds in length to the length to the permissible radial wear, saidradiation source and said radiation pick-up cooperating to produce asignal which cumulatively increases in magnitude as the radius of thewheel diminishes, means operable in response to each increase in thesignal to increase the speed of the motor, and means operated by themotor when the speed of the latter increases sufficiently to maintainthe surface speed of the wheel constant to render the last-named meansinoperative.

9. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining said surface speed of the wheelconstant as the wheel wears, comprising sensing means including afixedly mounted radiation source and a fixedly mounted radiation pick-updisposed adjacent opposite faces of the wheel, said radiation sourcehaving a point source spaced from the center of the wheel at a radiuscorresponding to the undiminished radius of the wheel prior to wear andsaid radiation pick-up having an elongated radiation sensing zonedisposed radially of the portion of the wheel worn away in use, saidradiation source and radiation pick-up cooperating to produce a signalof cumulatively increas ing magnitude as the radius of the wheeldiminshes, means operable in response to each increase in the signal toincrease the speed of the motor, and means operated by the motor whenthe speed of the latter increases sufficiently to maintain the surfacespeed of the wheel constant to render the last-named means inoperative.

10. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel and means for maintaining the surface speed of the wheelconstant as the wheel wears, comprising sensing means including afixedly mounted radiation source and a fixedly mounted radiation pick-updisposed adjacent opposite faces of the wheel, said radiation sourcehaving a point source situated at a distance from the center of thewheel corresponding to the undiminished radius of the wheel prior towear, and a spread which, projected on the face of the wheel, is atleast equal to the permissible amount of radial wear, said radiationpick-up having a sensitive zone disposed in a radial position relativeto the wheel which is at least as long as the projection of the spreadon the wheel, said components cooperating to produce a signal ofcumulatively increasing magnitude as the wheel diminishes in radius,means operable in response to each increase in the signal to increasethe speed of the motor, and means operated by the motor when the speedof the latter is increased sufficiently to maintain the surface speed ofthe wheel constant to render the last-named means inoperative.

11. In a grinding machine, a grinding wheel, a motor for driving thegrinding wheel, a source of power for supplying current to the motor andmeans for maintaining a constant surface speed as the wheel wears,comprising sensing means having components disposed at opposite faces ofthe wheel which operate to give a continuous signal, the magnitude ofwhich increases as the radius of the wheel diminishes, means operable byan increase in the signal to increase the current flow from said sourceto said motor, means operable to control the increase in speed of themotor in inverse proportion to the reduction in the radius of the Wheel,means operable by an increase in the speed of the motor sufficient tomaintain the surface speed of the wheel constant to render thelast-named means inoperative, and a safety device operable by anexcessive increase in speed to interrupt the fiow of current to themotor.

12. In a grinding machine, a grinding wheel, a motor for driving thewheel, means for supplying current to the motor including a normallyclosed switch and means for maintaining a constant surface speed as thewheel wears, comprising sensing means having components disposed atopposite faces of the wheel which operate to give a signal, themagnitude of which increases as the radius of the wheel diminishes, arheostat controlling the flow of the current from the source to thewheel motor, means operable by an increase in the signal to eifectmovement of the rheostat in the direction to increase the current flowto the motor, means responsive to an increase in speed of the motorsufiicient to maintain the surface speed of the wheel constant toterminate operation of the lastnamed means, and means operable by anexcessive increase in the speed of the motor to open said normallyclosed switch.

13. In a grinding machine, a grinding wheel, a motor for driving thewheel, a source of power for supplying current to the motor and meansfor maintaining a constant surface speed as the wheel wears, comprisingsensing means having components disposed at opposite faces of the wheelwhich operate to give a continuous signal, the magnitude of whichincreases as the radius of the wheel diminishes, means operable by thesignal to increase the current flow to the motor, feed-back meansoperable by the motor to render the last-named means inoperative whenthe increase in speed of the motor is sufficient to maintain the surfacespeed of the wheel constant, a linkage arranged to move linearly towardthe surface of the wheel as the speed of the motor increases, and meanscarried by the linkage operable by contact with the surface of the wheeldue to an excessive increase in speed of the motor to interrupt the flowof current from the source to the motor.

14. In a grinding machine, a grinding wheel, a motor for driving thewheel, a source of power for supplying current to the motor and meansfor maintaining a constant surface speed as the wheel wears, comprisingsensing means having components disposed at opposite faces of the wheelwhich operate to give a continuous signal of increasing magnitude as theradius of the wheel diminishes, means operable by each increase in themagnitude of the signal to increase the flow of current to the motor,feed-back means operable by the motor to render the last-named meansinoperative When the increase in speed of the motor is sufficient tomaintain the surface speed of the wheel constant, a link including apart situated at a predetermined distance from the surface of the wheelarranged to move linearly toward the surface of the wheel in proportionto the reduction in the radius of the wheel, said part of the linkagebeing movable into contact with the surface of the wheel if the increasein speed exceeds a proportionate reduction in the wheel, and a switchcarried by said part operable by contact with the wheel to interrupt thesupply of current to the motor.

References Cited in the file of this patent UNITED STATES PATENTS PriceJune 23, 1942 -Lonaberger Aug. 8, 1961 FOREIGN PATENTS Great BritainSept. 30, 1953

1. IN A GRINDING MACHINE, A GRINDING WHEEL, A MOTOR FOR DRIVING THEGRINDING WHEEL AND MEANS FOR MAINTAINING THE SURFACE SPEED OF THE WHEELCONSTANT AS THE WHEEL WEARS, COMPRISING AN ELONGATED SENSING DEVICEFIXEDLY SECURED RADIALLY OF THE GRINDING WHEEL AND OPERABLE, IN RESPONSETO A REDUCTION IN THE RADIUS OF THE WHEEL, TO PRODUCE A SIGNAL OFINCREASED MAGNITUDE, A COMPENSATOR RESPONSIVE TO AN INCREASE IN THESIGNAL TO INCREASE THE SPEED OF THE MOTOR, AND A FEED-BACK OPERATED BYTHE MOTOR IN RESPONSE TO AN INCREASE IN THE SPEED OF THE MOTORSUFFICIENT TO MAINTAIN THE SURFACE SPEED OF THE WHEEL CONSTANT TONULLIFY THE EFFECT OF THE INCREASE IN THE SIGNAL.